The present invention relates generally to an improved vessel for retaining cryogens, and more particularly to an improved flexible liner for compliably retaining a cryogen preferably within a generally rigid walled vessel. The flexible liner selected for the application are biodegradable polyester resins which possess the property of retaining flexibility at cryogenic temperatures as low as xe2x88x92210xc2x0 C. Biodegradable polyester resins of this type are commercially available.
Cryogenic vessels are widely used for a variety of applications, such as, for example, in applications for the packaging of frozen foods as well as for maintaining a low temperature ambient for transfer or shipping of articles including cryogens per se. Typical cryogens include, by way of example, liquid nitrogen, liquid air, liquified natural gas (LNG), and the like.
Because the volume of the film utilized in cryogenic applications is exceptionally large, it is desirable to utilize a material which possesses the physical properties required for the application, and at the same time, is biodegradable. A number of materials, while applicable for use as cryogenic liners are not suited for this application, inasmuch as the addition of biodegradable components may cause a deterioration of the physical properties of the film, thereby rendering it unsuited for the application. In addition, certain film components provide a limitation upon certain applications, particularly those in which direct and/or incidental contact with food is reasonably expected or anticipated.
In accordance with the present invention, flexible polyester liners have been developed which are biodegradable, and at the same, retain flexibility at cryogenic temperatures typically as low as about xe2x88x92210xc2x0 C. Such temperatures are, of course, compatible with cryogens such as liquid nitrogen (xe2x88x92210xc2x0 C.), liquid air (xe2x88x92200xc2x0 C.), liquified natural gas (LNG) (xe2x88x92182xc2x0 C.), as well as others such as solid carbon dioxide (dry ice). Several suitable biodegradable polyester resins are commercially available. One preferred resin is available commercially under the trade designation xe2x80x9cFBX-7011xe2x80x9d available from BASF of Parsipanny, N.J. Other suitable resins include a xe2x80x9cTonexe2x80x9d polymer, commercially available from the Union Carbide arm of Dow Chemical Co. under the trade designation xe2x80x9cP-787xe2x80x9d. An alternative polyester resin is available from Showa Denko of Japan under the trade designation xe2x80x9cBionollexe2x80x9d, and carrying the numerical suffix xe2x80x9c3001xe2x80x9d. A further alternative resin that is useful for certain cryogenic applications is available from Eastman Chemical of Rochester, N.Y. under the trade designation xe2x80x9cEastarxe2x80x9d. Polyesters suitable for use in connection with the present invention may also be prepared as the reaction product of a butylene diol such as 1,3-butylene glycol with a dibasic aliphatic acid to which a small quantity of an aromatic polyacid has been added to form mostly linear aliphatic polyesters useful in connection with the present invention.
In a typical application, the flexible biodegradable polyester film prepared from these resins is formed into a configuration to fit within a generally rigid walls of a cryogenic vessel. The walls are typically formed of a thin metallic sheet, and reinforced or supported by a durable but effective thermal insulation. Closed-cell polyurethane foam has been found to be useful in this regard, although other foams may be utilized as well. The entire insulation foam/metallic inner shell is placed within a more durable and rigid metallic outer shell for ease of handling and protection against damage due to impact and the like.
The cryogenic vessel may assume any of the normal configurations employed for these purposes. The description given herein is provided for ease in understanding the invention, and is not intended as a limitation upon the scope to which the invention is entitled.
Inasmuch as the volume of flexible film material utilized for cryogenic liners is large, and inasmuch as these materials are not readily reusable, particularly if employed in the food industry, their disposal is enhanced when the biodegradable feature is added. The utilization of biodegradable liners will serve to effectively reduce the need for landfill type disposal and the like, thereby providing an added measure of protection for the environment.
Therefore, it is a primary object of the present invention to provide an improved flexible liner for compliably retaining a cryogen within a cryogenic receiving vessel, wherein the flexible liner is a biodegradable polyester film which remains flexible at cryogenic temperatures as low as about xe2x88x92210xc2x0 C.
It is a further object of the present invention to provide an improved vessel adapted for receiving cryogens and adapted for controlled release of the cryogen in gaseous or liquid state, with the flexible liner compliably retaining the cryogen within the walls of a rigid vessel and being biodegradable and remaining flexible at cryogenic temperatures as low as about xe2x88x92210xc2x0 C.